1. Field of the Invention
The present invention relates to digitally controlled power supply apparatuses and production management systems equipped therewith, and in particular, a digitally controlled power supply apparatus having an automatic adjustment function of control parameters and a production management system equipped therewith.
2. Description of the Related Art
FIG. 12 illustrates a digitally controlled power supply apparatus having a common automatic adjustment function. Generally speaking, a digitally controlled power supply apparatus 501 having an automatic adjustment function for stable DC voltage output includes a switching device 511, a smoothing circuit 512, an analog-digital converter 513, a switching drive circuit 515, and a digital control unit 531. The switching device 511 is, for example, an FET (Field Effect Transistor) and, by being on/off driven in accordance with gate signals that it receives, converts a given input voltage Vin to output, for example, a pulse width modulated voltage. The smoothing circuit 512 is for smoothing the pulse width modulated voltage outputted by the switching device 511 and includes a choke coil L and an output capacitor Cout. The voltage outputted by the smoothing circuit 512 is outputted as DC power supply voltage Vout from the digitally controlled power supply apparatus 501, and applied to the load (not illustrated) connected to the digitally controlled power supply apparatus 501. The power supply voltage Vout outputted by the digitally controlled power supply apparatus 501 is fed back to the digital control unit 531 for automatic adjustment of the DC voltage output. The analog-digital converter 513 analog-digital converts the power supply voltage outputted by the smoothing circuit 512 to output power supply voltage digital data. The power supply voltage digital data outputted by the analog-digital converter 513 is inputted to the digital control unit 531. The digital control unit 531 includes a PID (Proportional-Integral-Derivative) controller 514, which performs PID control operation to the error between the setpoint and the power supply voltage digital data outputted by the analog-digital converter 513, and a control parameter adjuster 516, which dynamically performs automatic adjustment of the control parameters (proportional gain, derivative gain, and integral gain) used for the PID control operation by the PID controller 514 based on the history of fluctuations indicated in samplings of the power supply voltage digital data. The switching drive circuit 515 generates gate signals for on/off driving the switching device 511 based on the operation outcome of the PID controller 514, and outputs the signals to the gates of the switching device 511.
Such a digitally controlled power supply apparatus 501 may encounter fluctuations of the power supply voltage Vout outputted by the digitally controlled power supply apparatus 501 due to effects of various noises, aging of analog circuits inside, conditions of loads connected to the digitally controlled power supply apparatus 501 or other various factors. The control parameter adjuster 516 adjusts in real time the control parameters used for the PID control operation by the PID controller 514 and thereby ensures that the power supply voltage Vout outputted by the digitally controlled power supply apparatus 501 remains a stable DC voltage output. For example, the voltage outputted by the smoothing circuit 512 (i.e., the power supply voltage Vout outputted by the digitally controlled power supply apparatus 501) may more widely fluctuate as the capacitance of the output capacitor Cout in the smoothing circuit 512 decreases because of the aging of the output capacitor, but the real time adjustment by the control parameter adjuster 516 of the control parameters used for the PID control operation by the PID controller 514 ensures that the power supply voltage Vout outputted by the digitally controlled power supply apparatus 501 is kept substantially constant.
Various algorithms are known for automatic adjustment of the control parameters for PID controllers widely used for various control apparatuses including digitally controlled power supply apparatuses, such as the one described in Published Japanese Translation of PCT International Publication for Patent Application (Kohyo) No. 11-510932.
With various electric apparatuses equipped with a DC power supply, an abnormality in the DC power supply may bring various adverse effects on the apparatus and accompanying equipment; therefore, it is important to detect any malfunctions in the DC power supply.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2-145977 describes a power supply monitor apparatus for detecting abnormalities of a DC power supply by monitoring errors between the output voltages of the DC power supply and the standard voltage as well as the ripple voltages of the DC power supply.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2005-172653 describes an apparatus for monitoring the life of a power supply apparatus, exploiting the characteristics that the life of a power supply apparatus depends on the life of the electrolytic capacitor and that the ripple voltage of the output voltage of the power supply apparatus increases as the electrolytic capacitor approaches the end of its life.
For example, Japanese Unexamined Patent Publication (Kokai) No. 5-56629 describes a power conversion apparatus for industrial use that outputs maintenance information of the power conversion apparatus itself from the component deterioration detection circuit provided inside the power conversion apparatus and estimates the remaining lifespan of a component by comparing an estimation model for estimating the degree of deterioration (expected lifespan) with the operational conditions.
Further, in manufacturing plants, the machining and welding of workpieces (works) are carried out by using manufacturing machines such as a machine tool, an injection molding machine, or an arc welding robot. For machining workpieces, a plurality of manufacturing machines is grouped into manufacturing lines, e.g. manufacturing cells. In such a case, the manufacturing machines constituting the manufacturing cells are controlled by cell controllers via a communication network. The cell controllers are given an instruction of production plan by a production management apparatus placed on a still higher level. In such a production management system, there is an extensive demand for a power supply apparatus with high reliability and a capacity to supply stable DC voltage output as DC power supply for respective control systems of the manufacturing machines, the cell controllers, and the production management apparatus.
In a production management system having a cell controller that controls a plurality of manufacturing machines that constitute a manufacturing cell and a production management apparatus that gives an instruction of production plan to the cell controller, an abnormality in a single device may significantly impact the whole system and greatly decrease the productivity of the factory. This is especially relevant for power supply apparatuses because they are widely used as DC power supply for respective control systems of different pieces of equipment and an abnormality in a power supply apparatus directly leads to a malfunction in the control systems. To fully exploit the capacity of the digitally controlled power supply apparatus with an automatic adjustment function, which is a kind of power supply apparatus, for maintaining a stable DC output voltage, it is preferable to be able to detect the aging of the digitally controlled power supply apparatus to allow for an advance maintenance before an abnormality in the digitally controlled power supply apparatus occurs.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2-145977 and Japanese Unexamined Patent Publication (Kokai) No. 2005-172653 describe techniques for detecting an abnormality in the power supply by monitoring physical property values such as output voltage or ripple voltage, but the techniques require a separate hardware circuit for monitoring the physical property values and therefore have a drawback of additional expenses. In addition, although power supply performance tends to deteriorate gradually, the techniques in Japanese Unexamined Patent Publication (Kokai) No. 2-145977 and Japanese Unexamined Patent Publication (Kokai) No. 2005-172653 detect an abnormality only when there is a change in output voltage or ripple voltage, which makes the techniques unsuitable for advance maintenance, since it is highly likely that the abnormality have already impacted the devices equipped with the power supply or the system as a whole at the time of the detection of an abnormality. Furthermore, an inappropriately selected threshold to be used for abnormality detection may lead to an excessively early detection of abnormality or to a delayed detection of abnormality, resulting in a failure of maintenance.
For example, a technique described in Japanese Unexamined Patent Publication (Kokai) No. 5-56629 also requires a provision of a separate hardware circuit for monitoring operational conditions and has a drawback of additional expenses. This is especially relevant in that the more in detail the operational conditions are to be monitored, the more hardware that needs to be added. Furthermore, since the expected lifespan is determined by using an estimation model, when an inaccurate estimation model is used, an abnormality will occur in the power supply before the end of the expected lifespan as determined, which may result in an abrupt failure in the operation of the equipment provided with the power supply or the system as a whole.
Published Japanese Translation of PCT International Publication for Patent Application (Kohyo) No. 11-510932 discloses an algorithm for automatically adjusting the control parameters for PID controllers, but does not disclose a technique for detecting an occurrence of abnormality in a digitally controlled power supply apparatus for advance maintenance.
The capacity of a digitally controlled power supply apparatus of maintaining a stable DC output voltage can be fully exploited if the maintenance operator is notified in advance that an abnormality is likely to occur in a near future in the digitally controlled power supply apparatus to allow for the time for maintenance of the digitally controlled power supply apparatus before the abnormality actually occurs. This is especially relevant in a production management system that includes manufacturing machines, cell controllers and a production management apparatus, where a malfunction in any of the digitally controlled power supply apparatuses mounted in the equipment would significantly impact the whole system and greatly reduce the productivity of the factory, and therefore a great importance is attached to the preventive maintenance (advance maintenance) of the digitally controlled power supply apparatuses.